The experiments on enrichment of gold by bacteria indicate that bacteria have a very intense enrichment capacity for gold and act as an arrester of trace gold in sea water. Bacteria enrich gold in two forms: absorption and adsorption. Absorption means that gold comes inside organisms and is combined with the mercapto group of protein, whereras adsorption means that gold is ad-sorped outside organisms by aminoacid secreted by cell walls. Bacteria are organisms with very high vitality and reproductive capacity and huge productivity in nature. Bacteria, which are important geological agents for gold enrichment and exert effects on geological environments by their metabolism, are of important geochemical significance for the formation of gold-bearing black rocks.